The increased number of cancer cases reported in the United States, and, indeed, around the world, is a major concern. Currently there are only a handful of treatments available for specific types of cancer, and these provide no absolute guarantee of success. In order to be most effective, these treatments require not only an early detection of the malignancy, but a reliable assessment of the severity of the malignancy.
Cancer of the cervix is one of the most common malignancies in women and remains a significant public health problem throughout the world. In the United States alone, invasive cervical cancer accounts for approximately 19% of all gynecological cancers. In 1996, it was estimated that there were 14,700 newly diagnosed cases and 4900 deaths attributed to this disease (American Cancer Society, Cancer Facts & Figures 1996, Atlanta, Ga.: American Cancer Society, 1996). In many developing countries, where mass screening programs are not widely available, the clinical problem is more serious. Worldwide, the number of new cases is estimated to be 471,000 with a four-year survival rate of only 40% (Munoz et al., 1989, Epidemiology of Cervical Cancer In: “Human Papillomavirus”, New York, Oxford Press, pp 9-39; National Institutes of Health, Consensus Development Conference Statement on Cervical Cancer, Apr. 1-3, 1996).
In light of this, cervical cancer remains a highly preventable form of cancer when pre-invasive lesions are detected early. Cytological examination of Papanicolaou-stained cervical smears (also referred to as Pap smears or Pap tests) is currently the principle method for detecting cervical cancer and is the most cost-effective cancer screening test developed to date (Greenberg, M. D., et al., 1995, Clin Obstet Gynecol 38(3): 600-609). It has dramatically decreased the incidence and mortality rates of cervical cancer by more than 70% since it was introduced in the United States and many other countries of the world (Eddy D. M., 1990, Ann. Intern. Med. 113(3): 214-226). The abnormal morphologic changes of Pap tests described by The Bethesda System include ASCUS (atypical squamous cells of undetermined significance), AGUS (atypical glandular cells of undetermined significance), LSIL (low-grade squamous intraepithelial lesion), HSIL (high-grade squamous intraepithelial lesion), and squamous and adenocarcinoma (National Cancer Institute Workshop: The 1988 Bethesda System for reporting cervical/vaginal cytologic diagnosis. JAMA, 262(7): 931-934). The success of Pap tests is attributed mostly to the diagnosis and treatment of precancerous lesions.
Currently, management of patients with HSIL and more advanced diseases is relatively standard. Most women with such lesions undergo colposcopy and appropriately directed biopsies. If the histologic diagnosis is confirmed, ablative or excisional treatment such as electrosurgical loop excision procedure (LEEP), cryosurgery or conization is performed. However, management of ambiguous or low-grade cytological results (ASCUS and LSIL) is very controversial. This is mainly due to the nature of this morphology-based test, which inevitably leads to interobserver variability and some Pap test discordance with histological follow-up. It was reported that the mean sensitivity of primary Pap tests is approximately 58% and the accuracy of a repeat test is only about 66% (Fahey M. T., et al., 1995, Am. J. Epidemiol. 141: 680-689). The low sensitivity and poor reproducibility have complicated the management of ASCUS and LSIL patients. If an “accelerated repeat Pap test” is recommended for the follow-up of women with primary diagnosis of ASCUS or LSIL, patients will risk delay in diagnosis of potential high-grade lesions. However, if these patients are universally referred to colposcopy, the vast majority of women will be over treated. Only 5-10% of women with ASCUS have high-grade disease upon colposcopy, and more than 80% of LSIL will regress to normal or stay in their current state (Cox, J. T., 2000, Clinics in Laboratory Medicine. 20(2): 303-343, Ostor A. G., 1993, Int. J. Gynecol. Pathol. 12(2): 186-192).
AGUS represents a much greater risk than ASCUS or LSIL because cytology is less sensitive for this condition and the disease progresses more rapidly (Anderson M. C., 1995, Baillieres Clin. Obstet. Gynecol. 9:105). It was found that 9-54% of women with AGUS have biopsy-confirmed cervical intraepithelial neoplasias, 0-8% have biopsy-confirmed adenocarcinoma in situ (AIS), and less than 1-9% have invasive carcinoma (Wright, T. C., et al., 2002, JAMA, 287(16): 2120-2129). Due to the greater risk, all patients with AGUS are referred to colposcopy (Wright, T. C., et al., 2002).
The subjectivity of cervical cytology could be reduced by objective markers that determine the presence and severity of dysplastic cells. Since high-risk human papillomavirus (HPV) infection is strongly associated with cervical cancer development (Walboomers, J. M., et al., 1999, J. Pathol. 189: 12-19), HPV testing using methods like Hybrid Capture II (Digene Diagnostics, Silver Spring, Md.) or PCR appears to provide an objective measurement (Wick, M. J., 2000, Clinics in Laboratory Medicine, 20(2): 271-287). However, since the vast majority of HPV infections and the resulting squamous intraepithelial lesions regress spontaneously, especially in young women, HPV testing cannot specifically identify patients whose lesions will persist or progress to invasive carcinoma (Sasieni, P. D., 2000, J. Am. Med. Womens Assoc. 55(4): 216-219, Sasieni, P. D., 2000, Br. J. Cancer, 83(5): 561-565). As reported in the ASCUS-LSEL Triage Study (ALTS), 83% of woman with LSIL Pap results test positive for high-risk HPV types, a level too high to be useful for triage (Human papillomavirus testing for triage of women with cytologic evidence of low-grade squamous intraepithelial lesions: baseline data from a randomized trial. The Atypical Squamous Cells of Undetermined Significance/Low-Grade Squamous Intraepithelial Lesions Triage Study (ALTS) Group, 2000, J. Natl. Cancer Ist. 92:397-402). Although triage using HPV testing significantly improved the sensitivity for detecting HSIL in women with ASCUS Pap results, the specificity was comparable to using conventional cytology (Solomon, D., et al., 2001, J. Natl. Cancer Inst. 93(4): 293-299). A more desirable cervical screening marker would identify all cervical cancers, the majority of HSIL, and the small percentage of true precancers amongst patients with LSIL and ASCUS on Pap.
It is now well accepted that cervical carcinogenesis occurs in a step-wise fashion (Ried, T., et al., 1999, Genes Chromosomes Cancer, 25(3): 195-204). The transition of normal epithelium to preneoplastic lesions and invasive carcinoma occurs sequentially. The morphologically defined steps of dysplastic and malignant abnormalities are a reflection of cellular gene alterations during tumorgenesis. It would thus be desirable to provide biomarkers useful for the identification, assessment, prevention and therapy of cervical cancer.